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Sellards 8 Grigg, Inc. <br />THE EXISTING SIPHON SYSTEM <br />The existing siphon consists two reaches. Reach 1 consists of twin 4-inch pipes that <br />penetrate the Northwest intake portico plug. Outside of the plug, the twin lines enter a <br />manhole and combine into one 6-inch line. Reach 2 consists of a 6-inch line crossing <br />Interstate 70 and entering another manhole with the throttling valve. The line then <br />discharges through an upturned elbow to the River. At a minimum, bends occur in Reach <br />2 upstream of the highway, near the lower manhole at the turn toward the river, and at the <br />outfall. <br />The capacity of Reach 1 is too small with only the two feet of head used by Stover. If the <br />maximum flow rate is 350-gpm then a useful back up system must be able to carry that. <br />The water surface inside the mine required to drive Reach 1 is elevation 4768.27 instead <br />of 4764. Will the plug withstand that water level for an extended time period? An engineer <br />with geotechnical expertise may be required to answer that question. <br />On-the-other-hand, the capacity of Reach 2 is high relative to the demand. Reach 2 will <br />not flow full. The flowing water will tend to drag the air above the water along the pipe <br />thereby creating a reduced, subatmospheric pressure in the pipe. This reduced pressure <br />may cause the water surface to contact the top of the pipe at intervals. A pulsating flow <br />capable of damaging the system may result. To avoid this scenario S&G recommends <br />that a vent be added to the high point of the system to provide replacement air and <br />establish atmospheric pressure. To ensure enough air and to reduce excessive velocities <br />and attendant noise, the vent pipe should be at least 4-inches in diameter (Two vents may <br />be required if the 4-inch pipes are at the highest point in the system). A screen over the <br />vent should be provided to inhibit vandalism or the entry of wildlife into the system. <br />If a vent is not provided, siphoning may start and would eventually reduce the water <br />surface in the mine to below the intake causing a break in the siphon followed by filling the <br />mine. If siphoning self-starts the water surface in the mine will drop below elevation <br />4768.27 and will alternately drain to 4755-feet then fill to 4768.27-feet, where siphoning <br />may restart, resulting in a regular 13.27-foot variation of the water surface inside the mine. <br />Such a regular variation and alternate wetting and drying could result in deterioration of the <br />remaining structural elements of the mine. The recommended vent would prevent this <br />reciprocating action. <br />The same concerns listed for the proposed system, including screens both inside and <br />outside the mine to reduce the potential for blockage, apply to the existing siphon system. <br />CONCLUSIONS <br />Si3rG believes that the system as designed by J.E. Stover & Associates is a system that <br />will perform as designed. In order to prevent or reduce the chances of a malfunction, the <br />system can be improved with the addition of several features including the following: <br />1. A vent (with a minimum diameter of 6-inches to avoid whistling) at the high point of <br />the system, <br />390 Union Boulevard, 303.986.1444 <br />Suite 630 FAX 303.986.0994 <br />Lakewoo4 Colorado 80228 E-MAIL sandginc@earthlink.net <br />